Journal of Applied Microbiology 1999, 86, 331–336 Protective effect of bifidus milk on the experimental infection with Salmonella enteritidis subsp. typhimurium in conventional and gnotobiotic mice A.M. Silva, E.A. Bambirra 1 , A.L. Oliveira 2 , P.P. Souza, D.A. Gomes, E.C. Vieira 3 and J.R. Nicoli Departamento de Microbiologia, Instituto de Cie ˆ ncias Biolo ´ gicas, 1 Departamento de Anatomia Patolo ´ gica, Faculdade de Medicina, 2 Departamento de Tecnologia e Inspecc ¸ a ˜ o de Produtos de Origem Animal, Escola de Veterina ´ ria, and 3 Departamento de Bioquı ´ mica-Imunologia, Instituto de Cie ˆ ncias Biolo ´ gicas, Universidade Federal de Minas Gerais, Belo Horizonte MG, Brazil 6891/09/98: received 18 September 1998 and accepted 6 October 1998 A.M. SILVA, E.A. BAMBIRRA, A.L. OLIVEIRA, P.P. SOUZA, D.A. GOMES, E.C. VIEIRA AND J.R. NICOLI. 1999. The ability of Bifidobacterium bifidum from a commercial bifidus milk to antagonize Salmonella enteritidis subsp. typhimurium in vivo, and to reduce the pathological consequences for the host, was determined using conventional and gnotobiotic mice. Conventional animals received daily, by gavage, 0·1 ml bifidus milk containing about 10 9 cfu B. bifidum and germ-free animals received a single 0·1 ml dose. The conventional and gnotobiotic groups were challenged orally with 10 2 cfu of the pathogenic bacteria 5 and/or 10 d after the beginning of treatment. Control groups were treated with milk. Bifidus milk protected both animal models against the challenge with the pathogenic bacteria, as demonstrated by survival and histopathological data. However, to obtain the protective effect in gnotobiotic animals, the treatment had to be initiated 10 d before the challenge. In experimental and control gnotobiotic mice, Salm. enteritidis subsp. typhimurium became similarly established at levels ranging from 10 8 to 10 9 viable cells g -1 of faeces and remained at these high levels until the animals died or were sacrificed. It was concluded that the protection against Salm. enteritidis subsp. typhimurium observed in conventional and gnotobiotic mice treated with bifidus milk was not due to the reduction of the intestinal populations of the pathogenic bacteria. INTRODUCTION Gastrointestinal disease is often the consequence of a myriad factors which disturb the complex ecosystem of the gastro- intestinal tract. Antibiotics are the agents most commonly responsible for acute diarrhoea due to the loss of the pro- tective role of the normal intestinal microbiota against patho- genic organisms (Van der Waaij et al. 1982). Other aetiologies of diarrhoea are due to infection not associated with antibiotic use (e.g. toxigenic Escherichia coli, Salmonella enteritidis, Ent- Correspondence to: Dr Jacques Robert Nicoli, Departamento de Microbiologia, Instituto de Cie ˆncias Biolo ´gicas, Universidade Federal de Minas Gerais, C.P. 486, 30161–970, Belo Horizonte MG, Brazil (e-mail: jnicoli@mono.icb.ufmg.br). © 1999 The Society for Applied Microbiology amoeba histolytica, Giardia duodenalis, or viruses). In an effort to prevent or treat these cases, innovative approaches have been tried using live, biotherapeutic agents such as yeast (Saccharomyces) and bacterial species (Lactobacillus, Bifido- bacterium) or faecal enemas (Fuller 1992). Lactobacilli have the longest history as biotherapeutic agents (probiotics) and are still the most common ingredients among those intended for consumption by farm animals. This choice of probiotic bacteria seems appropriate because the normal gastrointestinal microbiota of these animals is par- ticularly rich in lactobacilli (Tannock 1997). Bifidobacterium spp. are now almost as common as lactobacilli in yoghurts and bifidus milk, presumably as a result of the realization that the human intestinal tract harbours larger and more stable